1. Technical Field
The invention disclosed herein generally relates to the removal of moisture from plant oils and liquid biofuels, also referred to as bioliquids. More specifically, this invention describes the use of glycerol as a solvent for the extraction of moisture from plant oils, including high value oils such as bio-oil (woody biomass based oil), and bioliquids, including biofuels such as biodiesel, and bio-kerosene, prior to and during storage.
2. Background Art
Glycerol is a clear, odorless, viscous liquid with a naturally sweet taste. It is derived from both natural and petrochemical feedstocks. Glycerol occurs in combined form (triglycerides) in animal fats and vegetable oils and is obtained from these fats and oils during transesterification including, for example, during biodiesel production. Glycerol is an inherent side product of this process along with a monovalent alcohol (methanol, ethanol, etc.) and fatty acid alkyl esters, as is shown in the formula set forth below.

Using stoichiometry, it can be calculated that 10% glycerol is formed during transesterification. However, this value holds for pure glycerol. The so-called crude glycerol that is a byproduct of biodiesel synthesis usually has a purity of between 55% and 90%, while the larger biodiesel plants tend to produce crude glycerol with the highest purities, often around 75%-80%. The remainder of the crude glycerol consists primarily of unconverted triglycerides, unconverted methanol, biodiesel, soaps and contamination. This dilution by impurities means that the actual amount of glycerol is much larger, between 100/90 (1.1) and 100/55 (1.8) times as much.
Typical composition data for biodiesel-derived glycerol are given in Table 1 below. Most of the contaminants can be traced back to the biodiesel synthesis process, for example the unreacted methanol that was not completely evaporated. The concentrations of Na and K indicate whether caustic soda (NaOH) or potash lye (KOH) was used as a catalyst for the transesterification. Alkali metals like Na, K, Ca and Mg are naturally present in vegetable oils. Sulfate and phosphate may remain from neutralization of the mixture with sulfuric or phosphoric acid.
TABLE 1Typical composition of crude glycerol from biodiesel productionPropertyValueUnitGlycerol content 77-90%wt %Ash content3.5-7%wt %Moisture content   0.1-13.5%wt %Lower calorific value14.9-17.5MJ/kgKinematic viscosity120mm2/s3-monopropylenediol  200-13,500ppmMethanol 0.01-3.0%wt %MONG 1.6-7.5%wt %pH4.5-7.4Sulfate0.01-1.04wt %Phosphate0.02-1.45wt %Acetate0.01-6.0 wt %Na0.4-20 g/kgK0.03-40 g/kgCa0.1-65 mg/kgMg0.02-55 mg/kgFe0.1-30 mg/kgMn  <0.5mg/kg
With the increase in renewable fuel production over the years, particularly biodiesel, comes an overabundance of off-grade glycerol. The supply of crude glycerol has nearly doubled while demand for the product has remained largely unchanged. This excess supply and limited demand has caused glycerol prices to remain depressed.
Glycerol continues to be one of the most versatile and valuable byproducts created during biodiesel production. Glycerol currently has innumerable known uses in many different industries ranging from foods, pharmaceuticals, and cosmetics to paints, coatings and other industrial types of applications. Businesses and researchers from around the globe are currently engaged in research and development projects, with the primary goal of developing economically viable technologies capable of utilizing this overabundant resource. Among these are: utilization of glycerol as a fuel to power generators; as a feedstock for plastics; and, as a carbon source for the production of omega-3 fatty acids. These new forms of commercialization should increase the profits of biodiesel producers by creating a new revenue streams.
However, in all the above-mentioned applications, whether as a reactant or as an additive, glycerol is principally used as a highly refined and purified product. Thus, if it is used in food, cosmetics and drugs, for example, further purifications are needed such as bleaching, deodorizing, and ion exchange to remove trace impurities. Purifying glycerol to this stage, however, is very costly and generally out of the range of economic feasibility for biodiesel plants. Hence, as more and more crude glycerol is generated by the biodiesel industry, it is very important that economical ways of utilizing crude or low-grade glycerol be explored to make biodiesel production more competitive in the growing global market. (Wolfson et al, 2009), for example, have successfully employed crude glycerol from triglyceride alcoholysis as a green solvent in base catalyzed aldol condensation and palladium catalyzed Heck carbon-carbon coupling without any purification.
It is an object of this present invention to identify commercial valuable uses for crude glycerol, including for example crude glycerol formed as a byproduct of bioliquid production, through its ability to remove excessive water from biodiesel fuels and plant oils.
Biodiesel may contain small but problematic quantities of water. Although, it is not miscible in water, biodiesel is hygroscopic (absorbs water from atmospheric moisture). Moisture saturation in biodiesel ranges from 0.10 to 0.17% wt (1,000 to 1,700 ppm) in the temperature range of 4 to 35° C., which is 15 to 25 times higher than that of fossil diesel (Thompson et. al, 2006). One of the reasons biodiesel tends to absorb water is the persistence of mono- and diglycerides left over from incomplete reaction. These molecules can act as an emulsifier, allowing water to mix with biodiesel. In addition, there may be water that is residual to processing or resulting from storage tank condensation.
The presence of water is a problem because it reduces the heat combustion of the bulk fuel, causes corrosion of vital system components (fuel and injector pumps, fuel lines, etc.), accelerates the growth of microbe colonies that can plug up fuel systems and causes pitting of the piston in diesel engines.
Current methods to reduce the water content in BDF below 500 ppm involves heating the wet biodiesel at 50° C. for 1 hour but this requires energy for heating (Nur et al, 2008). As energy is a significant global issue, and especially sensitive in the context of promoting the use of biodiesel, it is important to find alternative methods for removing water from biodiesel other than heating which is a high energy-consuming process.
A further object of the subject invention is to identify ways to remove moisture from stored biofuels and plant oils that are economically feasible and energy efficient.
It is a further object of the claimed invention to describe and disclose a simple and economically viable technology to absorb water from biodiesel, other bioliquids and plant oils using crude glycerol obtained as a byproduct of bioliquid production.